Data access object (DAO) in Java

In Java, a data access object (DAO) is a design pattern that provides an abstract interface for accessing data from a database. The DAO pattern separates the data access logic from the business logic and encapsulates it in a separate layer, which makes it easier to maintain and test the application.

A DAO typically includes methods for performing basic CRUD (create, read, update, delete) operations on the data, such as inserting, updating, and deleting records, as well as methods for querying the data.

Here is an example of a DAO interface in Java:

public interface UserDao {

    void insert(User user);

    void update(User user);

    void delete(int id);

    User findById(int id);

    List<User> findAll();

}

This example defines a UserDao interface with methods for inserting, updating, deleting, and finding users in a database.

To implement the DAO, you need to create a concrete class that implements the DAO interface and provides the implementation for the methods. The concrete class should handle the actual database interaction using JDBC or a persistence framework such as Hibernate.

Here is an example of a concrete DAO class that implements the UserDao interface:

public class UserDaoImpl implements UserDao {

    private Connection conn;

    public UserDaoImpl(Connection conn) {
        this.conn = conn;
    }

    @Override
    public void insert(User user) {
        // insert user into database using JDBC
    }

    @Override
    public void update(User user) {
        // update user in database using JDBC
    }

    @Override
    public void delete(int id) {
        // delete user from database using JDBC
    }

    @Override
    public User findById(int id) {
        // find user by id in database using JDBC
        return user;
    }

    @Override
    public List<User> findAll() {
        // find all users in database using JDBC
        return users;
    }

}

I hope this helps. Let me know if you have any questions.